1. Field of the Invention
The present invention relates to a storage unit that is installed newly into a computer system comprising a first storage unit and a host computer accessing the first storage unit, and an installation method thereof and an installation program therefor.
2. Related Art Statement
Recently, an amount of data treated by a computer is increasing by leaps, and accordingly storage capacity of a storage unit for storing data is increasing. As a result, costs of storage management in system management increase, and reduction of management costs becomes an important problem from the viewpoint of system operation.
When a new storage unit is installed into an existing computer system that comprises a host computer and a storage unit, two modes can be considered as a mode of installation, namely, a mode in which the old storage unit is used as ever, and the new storage unit is used together with the old storage unit, and a mode in which all the data on the old storage unit are migrated onto the new storage unit.
For example, as to the latter mode of installation, Japanese Patent Publication No. 10-508967 discloses a technique of migrating data of an old storage unit onto a new storage unit. According to the technique disclosed in the above document, data of a first device in the old storage unit are migrated onto a second device assigned to the new storage unit. Then, a host computer's access destination is changed from the existing first device to the new second device. An input-output request from the host computer to the existing first device is received by the new storage unit. With respect to a read request, a part whose migration is finished is read from the new second device, while a part that has not been migrated yet is read from the existing first device. Further, with respect to a write request, dual writing is performed toward both the first and second devices.
As described above, when a new storage unit is installed, it is possible to migrate data of a first device within an old storage unit to a second device within a new storage unit, without stopping input/output from/to a host computer.
However, in the case of the former mode of installation, where the new storage unit and the old storage unit are used side by side, there is a problem that, although generally the new storage unit has high function, high performance and high reliability in comparison with the old storage unit, it is impossible for data stored in the old storage unit to enjoy the merits of the new storage unit.
Further, in the case of the latter mode of installation, where all the data of the old storage unit are migrated onto the new storage unit, it is possible to enjoy the merits of the new storage unit by migrating the data stored in the old storage unit. However, there is a problem that, to migrate all the data of the old storage unit onto the new storage unit, the new storage unit must have more storage capacity than the old storage unit, and thus, the system installation cost is raised up.
Thus, as a compromise between them, it is possible to consider the following operation. Namely, the number of disk units mounted on a new storage unit is restrained to decrease initial investment, and the minimum data are migrated from an old storage unit to start system operation. At a stage in which a disk unit is added to the new storage unit, data is migrated from the old storage unit by an amount that the added disk unit allows. However, even by this compromise, data that can not be migrated because of storage capacity can not enjoy the merits of the new storage unit, similarly to the case where two storage units are used side by side.